Endoscopes and endoscopic video cameras are now widely used by physicians during surgery to view inside body cavities. In an endoscopic surgical procedure, small incisions, called portals, are made in a patient. An endoscope or endoscopic video camera is inserted in one of the portals. Surgical instruments used to perform specific surgical tasks are inserted into other portals. The surgeon views the surgical site through the endoscope or endoscopic video camera to determine how to manipulate the surgical instruments in order to accomplish the surgical procedure. An advantage of performing endoscopic surgery is that, since the portions of the body that are cut open are minimized, the portions of the body that need to heal after surgery are likewise reduced. Moreover, during an endoscopic surgical procedure, only relatively small portions of the patient's internal organs and tissues are exposed to the open environment. This minimal opening of the patient's body lessens the extent to which a patient's organs and tissues are open to infection.
Typically, an endoscopic video camera contains an optical focusing lens and a focusing device that can be adjusted to optimize images transmitted by the endoscopic video camera. The focusing device usually utilizes magnetic drives to move or rotate the focusing lens axially within the lens holder. As such, the lens holder is a small yet convoluted part of the endoscopic video camera. For example, the endoscopic video cameras described in U.S. Pat. No. 5,359,992 issued to Hori et al., and U.S. Pat. No. 5,056,902 issued to Chinnock et al. require the lens holders adapted to the mechanical linkages between the internal magnets and the lens, and the movement of the lens within the interior chamber in response to the rotation of external magnets located around the periphery of the interior chamber; and the endoscopic video cameras described in U.S. Pat. No. 5,978,161 issued to Lemke, U.S. Pat. No. 5,835,865 issued to Speier et al., and U.S. Pat. No. 5,706,143 issued to Hipp require lens holders having helical grooves, magnet seats and mechanical linkages to connect the internal magnets to the lens, or require the internal magnet to travel within a helical channel in order to convert the rotational movement of the internal magnets to linear movement of the lens.
In an effort to simplify the magnetic focusing device and to solve various shortcomings associated with the complicated endoscopic video cameras, U.S. Pat. Nos. 6,522,477 and 6,633,438, both issued to Anhalt, disclose endoscopic video cameras which do not require a mechanical linkage between the lens and internal magnets. The lens holders in Anhalt have the following structures, as illustrated in FIG. 1. A zoom lens holder 10a can be in the form of a raceway around the periphery of the lens (not shown) with a set of symmetrical protrusions or legs which are evenly spaced and extend proximally from the raceway in one direction which define the path of the lens during operation. A fixed lens holder 10b can be in the form of a raceway around the periphery of the lens with two sets of symmetrical protrusions or legs, with the first set of protrusions or legs extending proximally from the raceway in one direction, and the second set of protrusions or legs extending distally from the raceway in the opposite direction. Anhalt also discloses a simple lens holder 10c that does not contain any protrusions or legs extending from the raceway.
Because the lens holders play an important role in the performance of the endoscopic video cameras, it is critical that the lens holders be manufactured with precision.
Traditionally, the lens holders are manufactured from solid metal bar stocks by 100% machining, as illustrated in FIG. 2. This manufacturing method unavoidably results in high manufacturing cost in terms of material used (and wasted) and the machining time. Using this manufacturing method, it is difficult, if not impossible, to machine the lens holders with consistent precision. Therefore, the traditional 100% machining is not suitable for a high volume production of the lens holders.
In recent years, metal injection molding (“MIM”) processes have been used to manufacture various components in medical or optical instruments, as disclosed in U.S. Pat. Nos. 7,762,960, 6,514,269, 7,706,065 and 7,686,449; and U.S. Pat. Appln. No. 20060242813. The teachings of these patents are incorporated herein by references in its entirety.
In a typical MIM process, a metal powder is mixed with a binder to form a homogenous liquid mixture. The mixture is injected into a die or mold which is then subjected to high pressure to form a “green” metal blank, which typically is about 60% dense. The binder in the “green” metal blank is then burned off or removed chemically and the resulting skeleton, called “brown” metal blank, is sintered to near full density. Compared to the traditional 100% machining and other deposition techniques such as casting, stamping, and lithography, the MIM process greatly saves the material used for manufacturing and allows a high volume production with reasonable consistency in quality. The MIM process is also versatile at producing small components having complex internal and external shapes.
One long and continuing problem encountered with the MIM process is the shrinkage of metal blanks from the “green” stage. The shrinkage problem is generally more obvious in complex metal blanks, due to uneven shrinkages of the interior and exterior configurations after sintering. Another problem of the MIM process is that sintered metal blanks usually require a great extent of metal conditioning treatment in order to arrive at the desired dimensions of the final components. The metal conditioning treatment to sintered metal blanks is often referred as “secondary machining” or “post machining.” As with all machining, more secondary machining means more machining time and higher manufacturing cost.
To overcome the shrinkage problem encountered by typical the MIM process, U.S. Pat. No. 6,508,980 to Sachs, et al. (“Sachs”) provides a two-material sintering method. In contrast to a conventional method where a binder is removed and the powder particles themselves sintered together to provide a shrunken final component, in Sachs the material that joins the powder particles is provided as an independent material and there is no movement of the powder particles after they have been placed during sintering. Although the skeleton shrinkage may be avoided, the method in Sachs requires two different metal materials and the repeated steps of adding the second independent material into the matrix of the first material and binding the first and second materials.
What is desired, therefore, is an improved manufacturing method for an endoscopic camera component, such as a lens holder for an endoscope, which efficiently utilizes metal materials, minimizes secondary machining, shortens the overall manufacturing time, and increases consistency in the component quality. It is also desirable that such manufacturing method is sufficiently versatile to be applied to various types of lens holders and other similar types of metal components.